US20200044098A1 - Light detector - Google Patents
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- US20200044098A1 US20200044098A1 US16/583,674 US201916583674A US2020044098A1 US 20200044098 A1 US20200044098 A1 US 20200044098A1 US 201916583674 A US201916583674 A US 201916583674A US 2020044098 A1 US2020044098 A1 US 2020044098A1
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- 238000001514 detection method Methods 0.000 claims abstract description 114
- 230000015556 catabolic process Effects 0.000 claims abstract description 92
- 238000012544 monitoring process Methods 0.000 claims abstract description 75
- 238000010791 quenching Methods 0.000 claims description 19
- 230000000171 quenching effect Effects 0.000 claims description 19
- 230000004044 response Effects 0.000 claims description 6
- 238000005259 measurement Methods 0.000 description 20
- 230000035945 sensitivity Effects 0.000 description 17
- 230000008859 change Effects 0.000 description 6
- 238000010586 diagram Methods 0.000 description 6
- 238000005516 engineering process Methods 0.000 description 6
- 230000006870 function Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 230000003321 amplification Effects 0.000 description 2
- 230000008901 benefit Effects 0.000 description 2
- 230000007423 decrease Effects 0.000 description 2
- 230000007257 malfunction Effects 0.000 description 2
- 238000003199 nucleic acid amplification method Methods 0.000 description 2
- 230000000903 blocking effect Effects 0.000 description 1
- 239000003990 capacitor Substances 0.000 description 1
- 230000003247 decreasing effect Effects 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
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- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/02—Details
- H01L31/02016—Circuit arrangements of general character for the devices
- H01L31/02019—Circuit arrangements of general character for the devices for devices characterised by at least one potential jump barrier or surface barrier
- H01L31/02027—Circuit arrangements of general character for the devices for devices characterised by at least one potential jump barrier or surface barrier for devices working in avalanche mode
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
- G01S7/483—Details of pulse systems
- G01S7/486—Receivers
- G01S7/4861—Circuits for detection, sampling, integration or read-out
-
- H—ELECTRICITY
- H01—ELECTRIC ELEMENTS
- H01L—SEMICONDUCTOR DEVICES NOT COVERED BY CLASS H10
- H01L31/00—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof
- H01L31/08—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors
- H01L31/10—Semiconductor devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation and specially adapted either for the conversion of the energy of such radiation into electrical energy or for the control of electrical energy by such radiation; Processes or apparatus specially adapted for the manufacture or treatment thereof or of parts thereof; Details thereof in which radiation controls flow of current through the device, e.g. photoresistors characterised by at least one potential-jump barrier or surface barrier, e.g. phototransistors
-
- H—ELECTRICITY
- H03—ELECTRONIC CIRCUITRY
- H03F—AMPLIFIERS
- H03F3/00—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements
- H03F3/04—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only
- H03F3/08—Amplifiers with only discharge tubes or only semiconductor devices as amplifying elements with semiconductor devices only controlled by light
Definitions
- the present disclosure relates to a light detector that utilizes an avalanche effect.
- APD avalanche photodiode
- SPAD Single Photon Avalanche Diode
- the SPAD used by the light detector breaks down in response to the incidence of photons, and the light detector is configured to output a pulse signal in response to that the SPAD breaks down.
- the breakdown voltage of the SPAD changes with temperature.
- a light detector is provided to include a detection module, and a monitoring SPAD.
- the detection module includes an SPAD that is an avalanche photodiode operable in Geiger mode; the detection module is configured to perform light detection by applying, to the SPAD, a reverse bias voltage in a reverse direction.
- the monitoring SPAD has characteristics identical to characteristics of the SPAD in the detection module.
- the reverse bias voltage is generated to be applied to the SPAD in the detection module based on (i) a reference breakdown voltage set from a breakdown voltage generated across the monitoring SPAD in Geiger mode and (ii) a predetermined excess voltage.
- FIG. 1 is a block diagram showing a configuration of a light detector according to a first embodiment
- FIG. 2 is a block diagram showing a configuration of a light detector according to a second embodiment
- FIG. 3 is a block diagram showing a configuration of a light detector according to a third embodiment
- FIG. 4 is a block diagram showing a configuration of a light detector according to a fourth embodiment
- FIG. 5 is a block diagram showing a configuration of a light detector according to a fifth embodiment.
- FIG. 6 is a block diagram showing a configuration of a light detector according to a sixth embodiment.
- a light detector 1 A includes (i) a detection module 10 including a plurality of SPADs 2 and (ii) a monitoring SPAD 12 having the same configuration and the same characteristics as the SPAD 2 in the detection module 10 .
- module which may also be referred to as a circuit, may be configured to include circuitry (hardware circuit) as also described later in each description of the “module”.
- circuitry hardware circuit
- module may be also configured to include a central processing unit (CPU) along with memory storing instructions executed by the CPU, or both the circuitry and the CPU along with memory.
- CPU central processing unit
- the SPAD 2 and the monitoring SPAD 12 each are an APD operable in Geiger mode as described above.
- quenching resistors 4 are connected in series to the anodes of the plurality of SPADs 2 , respectively.
- the quenching resistor 4 generates a voltage drop due to the current flowing in the SPAD 2 when photons are incident on the SPAD 2 and the SPAD 2 breaks down, thereby stopping the Geiger discharge of the SPAD 2 .
- the quenching resistor 4 may be configured by a “resistor” which is a so-called common passive element, or may be configured by an active element such as a “transistor”.
- the quenching resistor 4 may also be referred to as a quenching element.
- each SPAD 2 breaks down, and the current generated in the quenching resistor 4 causes the voltage generated across the quenching resistor 4 to be input to a pulse converter 6 corresponding to each SPAD 2 .
- the pulse converter 6 is for outputting a pulse signal having a predetermined pulse width as a detection signal when photons are incident on the corresponding SPAD 2 .
- the pulse converter 6 When the voltage across the quenching resistor 4 is equal to or higher than a predetermined voltage, the pulse converter 6 generates a digital pulse “1”.
- the breakdown voltage of the SPAD 2 is estimated as a reference breakdown voltage V BD by using the monitoring SPAD 12 placed under the same environment as the detection module 10 . Then, based on the reference breakdown voltage V BD and a predetermined excess voltage V EX , a reverse bias voltage V SPAD is generated and applied to the cathode of each SPAD 2 in the detection module 10 .
- the light detector 1 A includes (i) a current source 14 for supplying a constant current to the monitoring SPAD 12 , (ii) a voltage source 16 for generating an excess voltage V EX , and (iii) a voltage generation module 18 for generating a reverse bias voltage V SPAD .
- the voltage generation module 18 is configured to generate the reverse bias voltage V SPAD by adding the breakdown voltage of the monitoring SPAD 12 as the reference breakdown voltage V BD to the excess voltage V EX from the voltage source 16 .
- the voltage generation module 18 only needs to generate the reverse bias voltage V SPAD based on the reference breakdown voltage V BD and the excess voltage V EX so that the excess voltage V EX is substantially constant; the respective voltages do not necessarily to be added directly.
- the current source 14 is capable of operating the monitoring SPAD 12 in Geiger mode by receiving the power supply voltage V B sufficiently higher than the breakdown voltage of the monitoring SPAD 12 and supplying a constant current I SPAD to the monitoring SPAD 12 .
- monitoring SPAD 12 is not connected to any quenching resistor like the SPAD 2 in the detection module 10 .
- the monitoring SPAD 12 is configured to continue the current flow once it is broken down.
- the reference breakdown voltage V BD which changes according to the temperature of the monitoring SPAD 12 , is always input to the voltage generation module 18 . Since the monitoring SPAD 12 has the same characteristics as the SPAD 2 included in the detection module 10 , the reference breakdown voltage V BD corresponds to the breakdown voltage of the SPAD 2 .
- a voltage obtained by adding a predetermined excess voltage V EX to the reference breakdown voltage V BD corresponding to the breakdown voltage of each SPAD 2 is always applied as the reverse bias voltage V SPAD to the cathode of each SPAD 2 in the detection module 10 .
- the detection sensitivity of each SPAD 2 in the detection module 10 becomes a constant detection sensitivity corresponding to the excess voltage V EX without being affected by the temperature change. Therefore, according to the present embodiment, the detection sensitivity of each of the SPADs 2 included in the detection module 10 can be temperature compensated, and the detection accuracy can be suppressed from changing due to the temperature.
- the monitoring SPAD 12 may be configured to receive light from the outside, as shown by a dotted line in FIG. 1 , the light shielding film 13 is provided to block the light from entering the monitoring SPAD 12 .
- the reference breakdown voltage V BD can be input to the voltage generation module 18 . Further, in this case, since the reference breakdown voltage V BD does not change under the influence of light incident on the monitoring SPAD 12 , the voltage generation module 18 can generate the reverse bias voltage V SPAD more stably.
- the light incident on the monitoring SPAD 12 may be smaller than the light incident on the detection module 10 . Also this case can provide substantially the same effect as in the case where the light shielding film 13 is provided on the monitoring SPAD 12 .
- the basic configuration of the light detector 1 B of a second embodiment is the same as that of the light detector 1 A of the first embodiment, and the difference from the first embodiment is the switch 22 and the voltage storage module 24 being added.
- the switch 22 is provided in the conduction path from the current source 14 to the monitoring SPAD 12 ; the switch 22 conducts or shuts off the conduction path according to the distance measurement operation signal from the distance measurement apparatus 20 using the light detector 1 B.
- the switch 22 is in an OFF state when the distance measurement apparatus 20 is operating or performing distance measurement based on a detection signal from the detection module 10 ; in contrast, the switch 22 is in an ON state when the distance measurement apparatus 20 stops the distance measurement.
- the monitoring SPAD 12 is supplied with current from the current source 14 and breaks down.
- the voltage storage module 24 sets and stores the breakdown voltage of the monitoring SPAD 12 as a reference breakdown voltage V BD , according to the distance measuring operation signal from the distance measurement apparatus 20 .
- the voltage storage module 24 outputs the stored reference breakdown voltage V BD to the voltage generation module 18 , thereby permitting the voltage generation module 18 to generate the reverse bias voltage V SPAD corresponding to the latest reference breakdown voltage V BD .
- the storage of the reference breakdown voltage V BD by the voltage storage module 24 may be performed by latching the reference breakdown voltage V BD to a storage element by charging a capacitor or the like, or by digitizing the reference breakdown voltage V BD and storing it in a memory.
- the monitoring SPAD 12 is operated when the distance measurement apparatus 20 , which is an external apparatus, stops the distance measurement. Therefore, when the detection module 10 is used for distance measurement operation, the operation of the monitoring SPAD 12 can be stopped; the increase in the power consumption of the light detector 1 B due to the current flowing to the monitoring SPAD 12 can be suppressed.
- the distance measurement apparatus 20 is mounted on a vehicle, and emits light for distance measurement forward in the traveling direction, and measures the distance to an obstacle present in front of the vehicle from the reflected light.
- the detection module 10 of this embodiment is thus used to receive the reflected light.
- the operations of the switch 22 and the voltage storage module 24 are switched according to the operation signal from the distance measurement apparatus 10 ; however, what switches the operations of the switch 22 and the voltage storage module 24 is not limited to the distance measurement apparatus 20 . That is, the switch 22 and the voltage storage module 24 may operate in accordance with an instruction from an external apparatus that uses the detection signal from the detection module 10 .
- the light detector 10 of a third embodiment has the same basic configuration as that of the light detector 1 A of the first embodiment.
- the difference from the first embodiment is that a plurality of monitoring SPADs 12 - 1 , 12 - 2 , . . . , 12 - n and a reference breakdown voltage setting module 30 (which may also be referred to as a calculation and selection module 30 ) of a reference breakdown voltage V BD are provided.
- the current source 14 is configured to supply n times the current I SPAD to be supplied to one monitoring SPAD (i.e., supply n ⁇ current I SPAD to a plurality of monitoring SPADs 12 - 1 , 12 - 2 , . . . , 12 - n ).
- the supplied current is distributed to the plurality of monitoring SPADs 12 - 1 , 12 - 2 , . . . , 12 - n , and each monitoring SPAD 12 - 1 , 12 - 2 , . . . , 12 - n operates in Geiger mode.
- breakdown voltages V BD1 , V BD2 , . . . , V BDn of the monitoring SPADs 12 - 1 , 12 - 2 , . . . , 12 - n are input to the reference breakdown voltage setting module 30 ; the reference breakdown voltage setting module 30 uses the breakdown voltages to generate the reference breakdown voltage V BD which is input to the voltage generation module 18 .
- the reference breakdown voltage setting module 30 selects a preset minimum value, maximum value, or median value from among a plurality of breakdown voltages V BD1 , V BD2 , . . . V BDn , or calculates an average value, thereby generating the reference breakdown voltage V BD to be input to the voltage generation module 18 .
- the monitoring SPAD 12 is configured to have the same characteristics as the SPAD 2 , it is not possible to eliminate the variation in the characteristics. If the variation in the characteristics of the monitoring SPAD 12 is large, the appropriate reference breakdown voltage V BD cannot be input to the voltage generation module 18 .
- the reference breakdown voltage V BD input to the voltage generation module 18 is generated using a plurality of monitoring SPADs 12 . Even if there are some of the monitoring SPADs 12 having large variations, an appropriate reference breakdown voltage V BD can be generated.
- the voltage generation module 18 can generate more appropriate reverse bias voltage V SPAD .
- the detection sensitivity of the SPAD 2 in the detection module 10 can be temperature compensated more favorably.
- the reference breakdown voltage setting module 30 is for generating more appropriate reference breakdown voltage V BD using a plurality of breakdown voltages V BD1 , V BD2 , . . . , V BDn . In general, it is better to select the median from among a plurality of the breakdown voltages V BD1 , V BD2 , . . . , V BDn .
- the basic configuration of the light detector 1 D of a fourth embodiment is the same as that of the light detector 1 A of the first embodiment.
- the difference from the first embodiment is that an excess voltage setting module 40 (which may also be referred to as a voltage control module 40 ) is provided to set the excess voltage V EX to be added to the reference breakdown voltage V BD in the voltage generation module 18 .
- the excess voltage setting module 40 is configured to take in the reference breakdown voltage V BD input to the voltage generation module 18 , and set the excess voltage V EX based on the reference breakdown voltage V BD .
- the reference breakdown voltage V BD is used as a detection signal of the temperature of the SPAD 2 ; the excess voltage V EX used to generate the reverse bias voltage V SPAD in the voltage generation module 18 is set according to the temperature.
- the detection sensitivity of each of the SPADs 2 included in the detection module 10 can be temperature compensated; it is possible to suppress a change in detection accuracy due to temperature.
- the excess voltage setting module 40 may be configured as a resistive voltage dividing circuit that changes the excess voltage V EX in proportion to the reference breakdown voltage V BD , for example, by dividing the reference breakdown voltage V BD by resistance division.
- the basic configuration of the light detector 1 E of a fifth embodiment is the same as that of the light detector 1 A of the first embodiment.
- the difference from the first embodiment is in (i) the configuration of the detection module 10 and (ii) addition of an output determination module 50 and a threshold setting module 52 (which may be also referred to as a threshold control module 52 ).
- the detection module 10 is configured as a so-called light receiving array by arranging a plurality of SPADs 2 in a lattice.
- a quenching resistor 4 and a pulse converter 6 are connected to each of the plurality of SPADs 2 provided in the detection module 10 as in the case shown in FIG. 1 . For this reason, when breakdown occurs due to photons entering each of the SPADs 2 , digital pulses are output from the pulse converters 6 as detection signals.
- the output determination module 50 counts the number (detection signal number) of detection signals respectively output from the plurality of SPADs 2 included in the detection module 10 through the pulse converters 6 . When the count value is equal to or greater than a predetermined threshold value, it is determined that light is detected by the detection module 10 .
- the output determination module 50 uses the detection module 10 as one pixel for light detection. The output determination module 50 determines that light is detected by the detection module 10 when the number of SPADs 2 that output detection signals among the plurality of SPADs 2 in the detection module 10 is equal to or greater than a threshold value.
- the output determination module 50 when determining that light is detected by the detection module 10 , the output determination module 50 outputs a trigger signal indicating that the light is detected by the detection module 10 .
- the threshold setting module 52 sets the threshold value used by the output determination module 50 for the determination based on the breakdown voltage of the monitoring SPAD 12 .
- the reverse bias voltage V SPAD applied to each SPAD 2 in the detection module 10 is generated by adding the predetermined excess voltage V EX to the reference breakdown voltage V BD , so the operating voltage of each SPAD 2 changes.
- the reverse bias voltage V SPAD is set by adding a predetermined excess voltage V EX to the reference breakdown voltage V BD .
- the reverse bias voltage V SPAD applied to the SPAD 2 changes. Then, when the reverse bias voltage V SPAD increases, the dark current flowing in the SPAD 2 increases, and this dark current causes the SPAD 2 to be easily broken down.
- the threshold value is set according to the reference breakdown voltage V BD in order to suppress the decrease in the detection accuracy of light by the detection module 10 even if the SPAD 2 easily malfunctions due to the dark current.
- the threshold setting module 52 may be configured to increase the threshold value when the reference breakdown voltage V BD increases.
- the quenching resistor 4 is connected to the anode of each SPAD 2 .
- a detection signal is output from the connection point between the anode of each SPAD 2 and the corresponding quenching resistor 4 via the pulse converter 6 .
- the voltage generation module 18 adds the reference breakdown voltage V BD and the predetermined excess voltage V EX to generate a reverse bias voltage V SPAD having a potential higher than that of the anode of each SPAD 2 , and the reverse bias voltage VS PAD is applied to the cathode of each SPAD 2 .
- the reverse bias voltage V SPAD is preferably a positive potential.
- the quenching resistance 4 is connected to the cathode of each SPAD 2 .
- the detection signal is output from the connection point between the cathode of each SPAD 2 and the corresponding quenching resistor 4 through the pulse converter 6 .
- the power supply voltage V B is applied to the cathode of the SPAD 2 through the quenching resistor 4 .
- the potential of the anode of the SPAD 2 needs to be lower than that of the cathode by the reverse bias voltage.
- the power supply voltage V B is applied to the cathode of the monitoring SPAD 12 as in the SPAD 2 in the detection module 10 .
- the current source 14 is connected to the anode of the monitoring SPAD 12 so as to flow current from the anode to the ground.
- the voltage generation module 18 takes in a negative reference breakdown voltage ⁇ V BD lower than the power supply voltage V B from the anode of the monitoring SPAD 12 .
- a negative excess voltage ⁇ V EX obtained from the negative electrode side of the voltage source 16 is added to the negative reference breakdown voltage ⁇ V BD .
- the negative reference breakdown voltage ⁇ V BD and the negative excess voltage ⁇ V EX are added.
- the reverse bias voltage ⁇ V SPAD is thereby generated which is lower in potential than the cathode of the SPAD 2 .
- the generated reverse bias voltage ⁇ V SPAD is applied to the anode of each SPAD 2 in the detection module 10 .
- the reverse bias voltage ⁇ V SPAD is preferably a negative potential.
- a reverse bias voltage V SPAD obtained by adding the excess voltage V EX to the reference breakdown voltage V BD is applied between the cathode and the anode of each SPAD 2 in the detection module 10 .
- the monitoring SPAD 12 may be provided with the light shielding film 13 for blocking or suppressing the incidence of light.
- the light shielding film 13 may be provided on the monitoring SPAD 12 to shielding light.
- the detection module 10 has been described as being provided with a plurality of SPADs 2 . Even in the case where one SPAD 2 is provided in the detection module 10 , the reduction in the detection sensitivity of the detection module 10 can be suppressed if configured as in the above-described embodiments.
- a plurality of functions of one element in the above embodiments may be implemented by a plurality of elements, or one function of one element may be implemented by a plurality of elements. Further, a plurality of functions of a plurality of elements may be implemented by one element, or one function implemented by a plurality of elements may be implemented by one element. A part of the configuration of the above embodiment may be omitted. At least a part of the configuration of the above embodiments may be added to or replaced with the configuration of another one of the above embodiments.
- a related art discloses a technology of a light detector using an avalanche photodiode (hereinafter referred to as APD).
- the technology performs temperature compensation of the APD by using a reverse biased reference junction structure which has a temperature characteristic of the current amplification factor that is almost the same as that of the APD.
- This light detector uses a transistor having a current injection junction structure for injecting a reference current into the reference junction structure, and controls a multiplication factor of the APD by controlling the voltage applied to the APD and the reference junction structure so as to keep the amplification factor of the reference current at a predetermined value.
- the above technology performs the temperature compensation control of the APD by controlling the multiplication factor of the APD. It is thus effective in the linear mode operated by applying a reverse bias voltage less than the breakdown voltage to the APD.
- SPAD Single Photon Avalanche Diode
- the SPAD used by the light detector breaks down in response to the incidence of photons, and the light detector is configured to output a pulse signal having a predetermined pulse width in response to that the SPAD breaks down.
- the output of the light detector using SPAD is “1” or “0”; this type of light detector has no concept of controlling the multiplication factor. For this reason, it is difficult to temperature compensate the detection sensitivity of an SPAD by using the above technique.
- a light detector is provided to include a detection module, a monitoring SPAD, a current source, and a voltage generation module.
- the detection module includes an SPAD that is an avalanche photodiode operable in Geiger mode; the detection module is configured to perform light detection by applying, to the SPAD, a reverse bias voltage in a reverse direction.
- the monitoring SPAD has characteristics identical to characteristics of the SPAD in the detection module.
- the current source which may be connected with the monitoring SPAD, is configured to supply a constant current to the monitoring SPAD so as to operate the monitoring SPAD in Geiger mode.
- the voltage generation module which may be connected with the monitoring SPAD, is configured to generate the reverse bias voltage to be applied to the SPAD in the detection module based on (i) a reference breakdown voltage set from a breakdown voltage generated across the monitoring SPAD and (ii) a predetermined excess voltage.
- the SPAD in the detection module receives a reverse bias voltage; the reverse bias voltage is generated based on (i) the reference breakdown voltage estimated to be a breakdown voltage when the SPAD breaks down due to incidence of photons, and (ii) a predetermined excess voltage.
- the excess voltage becomes a substantially predetermined constant voltage. It is thus possible to stabilize the detection sensitivity of photons by the SPAD.
- a reverse bias voltage exceeding the breakdown voltage is applied to the SPAD; in response to that photons are incident on an SPAD, a detection signal is output based on the current flowing when the SPAD breaks down.
- the breakdown voltage of the SPAD changes with temperature. Specifically, the breakdown voltage is higher as the temperature is higher. Therefore, if the reverse bias voltage applied to the SPAD is maintained to be constant, the excess voltage, which is the excess voltage obtained by subtracting the breakdown voltage from the constant reverse bias voltage, becomes lower (decreases) as the temperature becomes higher (increases). The detection sensitivity of the SPAD thereby changes with voltage change of the excess voltage.
- the breakdown voltage of the SPAD in the detection module is estimated as the reference breakdown voltage using the monitoring SPAD.
- the reverse bias voltage is set based on the reference breakdown voltage and the desired excess voltage.
- the light detector of the present disclosure enables the temperature compensation of the detection sensitivity of the SPAD that is included in the detection module, further enabling the light detection with a desired detection sensitivity without being affected by the temperature change of the SPAD.
Abstract
Description
- The present application is a continuation application of International Patent Application No. PCT/JP2018/013818 filed on Mar. 30, 2018, which designated the U.S. and claims the benefit of priority from Japanese Patent Application No. 2017-071412 filed on Mar. 31, 2017 and Japanese Paten Application No. 2018-022999 filed on Feb. 13, 2018. The entire disclosures of all of the above applications are incorporated herein by reference.
- The present disclosure relates to a light detector that utilizes an avalanche effect.
- There is known a technology of a light detector using an avalanche photodiode (hereinafter referred to as APD). Further, there is a light detector that operates the APD in Geiger mode. The APD operating in Geiger mode is called SPAD, which is an abbreviation of Single Photon Avalanche Diode. The SPAD used by the light detector breaks down in response to the incidence of photons, and the light detector is configured to output a pulse signal in response to that the SPAD breaks down. The breakdown voltage of the SPAD changes with temperature.
- According to an embodiment of the present disclosure, a light detector is provided to include a detection module, and a monitoring SPAD.
- The detection module includes an SPAD that is an avalanche photodiode operable in Geiger mode; the detection module is configured to perform light detection by applying, to the SPAD, a reverse bias voltage in a reverse direction. The monitoring SPAD has characteristics identical to characteristics of the SPAD in the detection module. The reverse bias voltage is generated to be applied to the SPAD in the detection module based on (i) a reference breakdown voltage set from a breakdown voltage generated across the monitoring SPAD in Geiger mode and (ii) a predetermined excess voltage.
- The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings:
-
FIG. 1 is a block diagram showing a configuration of a light detector according to a first embodiment; -
FIG. 2 is a block diagram showing a configuration of a light detector according to a second embodiment; -
FIG. 3 is a block diagram showing a configuration of a light detector according to a third embodiment; -
FIG. 4 is a block diagram showing a configuration of a light detector according to a fourth embodiment; -
FIG. 5 is a block diagram showing a configuration of a light detector according to a fifth embodiment; and -
FIG. 6 is a block diagram showing a configuration of a light detector according to a sixth embodiment. - Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.
- As shown in
FIG. 1 , alight detector 1A according to a first embodiment includes (i) adetection module 10 including a plurality ofSPADs 2 and (ii) a monitoringSPAD 12 having the same configuration and the same characteristics as theSPAD 2 in thedetection module 10. For instance, “module”, which may also be referred to as a circuit, may be configured to include circuitry (hardware circuit) as also described later in each description of the “module”. However, there is no need to be limited thereto. That is, “module” may be also configured to include a central processing unit (CPU) along with memory storing instructions executed by the CPU, or both the circuitry and the CPU along with memory. - The SPAD 2 and the
monitoring SPAD 12 each are an APD operable in Geiger mode as described above. In thedetection module 10,quenching resistors 4 are connected in series to the anodes of the plurality ofSPADs 2, respectively. - The
quenching resistor 4 generates a voltage drop due to the current flowing in theSPAD 2 when photons are incident on theSPAD 2 and theSPAD 2 breaks down, thereby stopping the Geiger discharge of theSPAD 2. Thequenching resistor 4 may be configured by a “resistor” which is a so-called common passive element, or may be configured by an active element such as a “transistor”. Thequenching resistor 4 may also be referred to as a quenching element. - Then, in the
detection module 10, eachSPAD 2 breaks down, and the current generated in thequenching resistor 4 causes the voltage generated across thequenching resistor 4 to be input to apulse converter 6 corresponding to eachSPAD 2. - The
pulse converter 6 is for outputting a pulse signal having a predetermined pulse width as a detection signal when photons are incident on thecorresponding SPAD 2. When the voltage across thequenching resistor 4 is equal to or higher than a predetermined voltage, thepulse converter 6 generates a digital pulse “1”. - Note that in order to operate the
detection module 10, it is necessary to apply a reverse bias voltage VSPAD higher than the breakdown voltage to eachSPAD 2 in the (reverse) direction reverse to the forward direction. When the reverse bias voltage VSPAD is constant, the detection sensitivity of eachSPAD 2 changes with temperature. - Therefore, in the present embodiment, the breakdown voltage of the
SPAD 2 is estimated as a reference breakdown voltage VBD by using themonitoring SPAD 12 placed under the same environment as thedetection module 10. Then, based on the reference breakdown voltage VBD and a predetermined excess voltage VEX, a reverse bias voltage VSPAD is generated and applied to the cathode of eachSPAD 2 in thedetection module 10. - Therefore, the
light detector 1A includes (i) acurrent source 14 for supplying a constant current to themonitoring SPAD 12, (ii) avoltage source 16 for generating an excess voltage VEX, and (iii) avoltage generation module 18 for generating a reverse bias voltage VSPAD. - The
voltage generation module 18 is configured to generate the reverse bias voltage VSPAD by adding the breakdown voltage of themonitoring SPAD 12 as the reference breakdown voltage VBD to the excess voltage VEX from thevoltage source 16. - The
voltage generation module 18 only needs to generate the reverse bias voltage VSPAD based on the reference breakdown voltage VBD and the excess voltage VEX so that the excess voltage VEX is substantially constant; the respective voltages do not necessarily to be added directly. - Next, the
current source 14 is capable of operating themonitoring SPAD 12 in Geiger mode by receiving the power supply voltage VB sufficiently higher than the breakdown voltage of themonitoring SPAD 12 and supplying a constant current ISPAD to themonitoring SPAD 12. - Note that the monitoring SPAD 12 is not connected to any quenching resistor like the
SPAD 2 in thedetection module 10. The monitoring SPAD 12 is configured to continue the current flow once it is broken down. - Therefore, the reference breakdown voltage VBD, which changes according to the temperature of the
monitoring SPAD 12, is always input to thevoltage generation module 18. Since themonitoring SPAD 12 has the same characteristics as theSPAD 2 included in thedetection module 10, the reference breakdown voltage VBD corresponds to the breakdown voltage of theSPAD 2. - Therefore, a voltage obtained by adding a predetermined excess voltage VEX to the reference breakdown voltage VBD corresponding to the breakdown voltage of each
SPAD 2 is always applied as the reverse bias voltage VSPAD to the cathode of eachSPAD 2 in thedetection module 10. - Therefore, in the
light detector 1A of the present embodiment, the detection sensitivity of eachSPAD 2 in thedetection module 10 becomes a constant detection sensitivity corresponding to the excess voltage VEX without being affected by the temperature change. Therefore, according to the present embodiment, the detection sensitivity of each of theSPADs 2 included in thedetection module 10 can be temperature compensated, and the detection accuracy can be suppressed from changing due to the temperature. - Although the monitoring SPAD 12 may be configured to receive light from the outside, as shown by a dotted line in
FIG. 1 , thelight shielding film 13 is provided to block the light from entering themonitoring SPAD 12. - Even in this case, since the
monitoring SPAD 12 breaks down due to noise, the reference breakdown voltage VBD can be input to thevoltage generation module 18. Further, in this case, since the reference breakdown voltage VBD does not change under the influence of light incident on themonitoring SPAD 12, thevoltage generation module 18 can generate the reverse bias voltage VSPAD more stably. - Further, by disposing the
monitoring SPAD 12 on the back side of thedetection module 10, for example, the light incident on themonitoring SPAD 12 may be smaller than the light incident on thedetection module 10. Also this case can provide substantially the same effect as in the case where thelight shielding film 13 is provided on the monitoring SPAD 12. - As shown in
FIG. 2 , the basic configuration of thelight detector 1B of a second embodiment is the same as that of thelight detector 1A of the first embodiment, and the difference from the first embodiment is theswitch 22 and thevoltage storage module 24 being added. - Therefore, in the present embodiment, the same elements as those in the first embodiment are denoted by the same reference signs in the drawings, and detailed descriptions thereof will be omitted.
- As shown in
FIG. 2 , theswitch 22 is provided in the conduction path from thecurrent source 14 to themonitoring SPAD 12; theswitch 22 conducts or shuts off the conduction path according to the distance measurement operation signal from thedistance measurement apparatus 20 using thelight detector 1B. - The
switch 22 is in an OFF state when thedistance measurement apparatus 20 is operating or performing distance measurement based on a detection signal from thedetection module 10; in contrast, theswitch 22 is in an ON state when thedistance measurement apparatus 20 stops the distance measurement. - Therefore, when the
distance measurement apparatus 20 stops the distance measurement, the monitoringSPAD 12 is supplied with current from thecurrent source 14 and breaks down. - Therefore, when the
distance measurement apparatus 20 stops the distance measurement, thevoltage storage module 24 sets and stores the breakdown voltage of the monitoringSPAD 12 as a reference breakdown voltage VBD, according to the distance measuring operation signal from thedistance measurement apparatus 20. - Then, when the
distance measurement apparatus 20 starts the distance measurement, thevoltage storage module 24 outputs the stored reference breakdown voltage VBD to thevoltage generation module 18, thereby permitting thevoltage generation module 18 to generate the reverse bias voltage VSPAD corresponding to the latest reference breakdown voltage VBD. - The storage of the reference breakdown voltage VBD by the
voltage storage module 24 may be performed by latching the reference breakdown voltage VBD to a storage element by charging a capacitor or the like, or by digitizing the reference breakdown voltage VBD and storing it in a memory. - As described above, according to the
light detector 1B of the present embodiment, the monitoringSPAD 12 is operated when thedistance measurement apparatus 20, which is an external apparatus, stops the distance measurement. Therefore, when thedetection module 10 is used for distance measurement operation, the operation of the monitoringSPAD 12 can be stopped; the increase in the power consumption of thelight detector 1B due to the current flowing to themonitoring SPAD 12 can be suppressed. - The
distance measurement apparatus 20 is mounted on a vehicle, and emits light for distance measurement forward in the traveling direction, and measures the distance to an obstacle present in front of the vehicle from the reflected light. Thedetection module 10 of this embodiment is thus used to receive the reflected light. - Note that in the present embodiment, the operations of the
switch 22 and thevoltage storage module 24 are switched according to the operation signal from thedistance measurement apparatus 10; however, what switches the operations of theswitch 22 and thevoltage storage module 24 is not limited to thedistance measurement apparatus 20. That is, theswitch 22 and thevoltage storage module 24 may operate in accordance with an instruction from an external apparatus that uses the detection signal from thedetection module 10. - As shown in
FIG. 3 , thelight detector 10 of a third embodiment has the same basic configuration as that of thelight detector 1A of the first embodiment. The difference from the first embodiment is that a plurality of monitoring SPADs 12-1, 12-2, . . . , 12-n and a reference breakdown voltage setting module 30 (which may also be referred to as a calculation and selection module 30) of a reference breakdown voltage VBD are provided. - Therefore, in the present embodiment, the same elements as those in the first embodiment are denoted by the same reference signs in the drawings, and detailed descriptions thereof will be omitted. As shown in
FIG. 3 , in order to operate a plurality of monitoring SPADs 12-1, 12-2, . . . , 12-n in Geiger mode, thecurrent source 14 is configured to supply n times the current ISPAD to be supplied to one monitoring SPAD (i.e., supply n×current ISPAD to a plurality of monitoring SPADs 12-1, 12-2, . . . , 12-n). Then, the supplied current is distributed to the plurality of monitoring SPADs 12-1, 12-2, . . . , 12-n, and each monitoring SPAD 12-1, 12-2, . . . , 12-n operates in Geiger mode. - Further, breakdown voltages VBD1, VBD2, . . . , VBDn of the monitoring SPADs 12-1, 12-2, . . . , 12-n are input to the reference breakdown
voltage setting module 30; the reference breakdownvoltage setting module 30 uses the breakdown voltages to generate the reference breakdown voltage VBD which is input to thevoltage generation module 18. - The reference breakdown
voltage setting module 30 selects a preset minimum value, maximum value, or median value from among a plurality of breakdown voltages VBD1, VBD2, . . . VBDn, or calculates an average value, thereby generating the reference breakdown voltage VBD to be input to thevoltage generation module 18. - This is because even if the monitoring
SPAD 12 is configured to have the same characteristics as theSPAD 2, it is not possible to eliminate the variation in the characteristics. If the variation in the characteristics of the monitoringSPAD 12 is large, the appropriate reference breakdown voltage VBD cannot be input to thevoltage generation module 18. - That is, in the present embodiment, the reference breakdown voltage VBD input to the
voltage generation module 18 is generated using a plurality ofmonitoring SPADs 12. Even if there are some of themonitoring SPADs 12 having large variations, an appropriate reference breakdown voltage VBD can be generated. - Therefore, according to the present embodiment, the
voltage generation module 18 can generate more appropriate reverse bias voltage VSPAD. The detection sensitivity of theSPAD 2 in thedetection module 10 can be temperature compensated more favorably. - The reference breakdown
voltage setting module 30 is for generating more appropriate reference breakdown voltage VBD using a plurality of breakdown voltages VBD1, VBD2, . . . , VBDn. In general, it is better to select the median from among a plurality of the breakdown voltages VBD1, VBD2, . . . , VBDn. - As shown in
FIG. 4 , the basic configuration of thelight detector 1D of a fourth embodiment is the same as that of thelight detector 1A of the first embodiment. The difference from the first embodiment is that an excess voltage setting module 40 (which may also be referred to as a voltage control module 40) is provided to set the excess voltage VEX to be added to the reference breakdown voltage VBD in thevoltage generation module 18. - Therefore, in the present embodiment, the same elements as those in the first embodiment are denoted by the same reference signs in the drawings, and detailed descriptions thereof will be omitted. As shown in
FIG. 4 , the excessvoltage setting module 40 is configured to take in the reference breakdown voltage VBD input to thevoltage generation module 18, and set the excess voltage VEX based on the reference breakdown voltage VBD. - This is because the characteristic of the
SPAD 2 changes with temperature, so that it is conceivable that the excess voltage VEX should also be adjusted according to the temperature in order to control the detection sensitivity to a desired detection sensitivity. - That is, in the present embodiment, the reference breakdown voltage VBD is used as a detection signal of the temperature of the
SPAD 2; the excess voltage VEX used to generate the reverse bias voltage VSPAD in thevoltage generation module 18 is set according to the temperature. - As a result, also in the
light detector 1D of this embodiment, as in thelight detectors 1A to 1C of each of the above embodiments, the detection sensitivity of each of theSPADs 2 included in thedetection module 10 can be temperature compensated; it is possible to suppress a change in detection accuracy due to temperature. - The excess
voltage setting module 40 may be configured as a resistive voltage dividing circuit that changes the excess voltage VEX in proportion to the reference breakdown voltage VBD, for example, by dividing the reference breakdown voltage VBD by resistance division. - As shown in
FIG. 5 , the basic configuration of thelight detector 1E of a fifth embodiment is the same as that of thelight detector 1A of the first embodiment. The difference from the first embodiment is in (i) the configuration of thedetection module 10 and (ii) addition of anoutput determination module 50 and a threshold setting module 52 (which may be also referred to as a threshold control module 52). - Therefore, in the present embodiment, the same elements as those in the first embodiment are denoted by the same reference signs in the drawings, and detailed descriptions thereof will be omitted. The
detection module 10 is configured as a so-called light receiving array by arranging a plurality ofSPADs 2 in a lattice. - Note that a quenching
resistor 4 and apulse converter 6 are connected to each of the plurality ofSPADs 2 provided in thedetection module 10 as in the case shown inFIG. 1 . For this reason, when breakdown occurs due to photons entering each of theSPADs 2, digital pulses are output from thepulse converters 6 as detection signals. - The
output determination module 50 counts the number (detection signal number) of detection signals respectively output from the plurality ofSPADs 2 included in thedetection module 10 through thepulse converters 6. When the count value is equal to or greater than a predetermined threshold value, it is determined that light is detected by thedetection module 10. - This is because a
certain SPAD 2 may be broken down due to noise and output a detection signal through thepulse converter 6. That is, theoutput determination module 50 uses thedetection module 10 as one pixel for light detection. Theoutput determination module 50 determines that light is detected by thedetection module 10 when the number ofSPADs 2 that output detection signals among the plurality ofSPADs 2 in thedetection module 10 is equal to or greater than a threshold value. - Then, when determining that light is detected by the
detection module 10, theoutput determination module 50 outputs a trigger signal indicating that the light is detected by thedetection module 10. In contrast, thethreshold setting module 52 sets the threshold value used by theoutput determination module 50 for the determination based on the breakdown voltage of the monitoringSPAD 12. - This is because, in the present embodiment, the reverse bias voltage VSPAD applied to each
SPAD 2 in thedetection module 10 is generated by adding the predetermined excess voltage VEX to the reference breakdown voltage VBD, so the operating voltage of eachSPAD 2 changes. - That is, the reverse bias voltage VSPAD is set by adding a predetermined excess voltage VEX to the reference breakdown voltage VBD. In this case, although the detection sensitivity of each
SPAD 2 can be suppressed from decreasing due to temperature, the reverse bias voltage VSPAD applied to theSPAD 2 changes. Then, when the reverse bias voltage VSPAD increases, the dark current flowing in theSPAD 2 increases, and this dark current causes theSPAD 2 to be easily broken down. - Therefore, in the present embodiment, the threshold value is set according to the reference breakdown voltage VBD in order to suppress the decrease in the detection accuracy of light by the
detection module 10 even if theSPAD 2 easily malfunctions due to the dark current. - Note that if the reference breakdown voltage VBD increases with the temperature increases, the reverse bias voltage VSPAD also increases and the
SPAD 2 is easily malfunction. Thethreshold setting module 52 may be configured to increase the threshold value when the reference breakdown voltage VBD increases. - In the
light detectors 1A to 1E according to the first to fifth embodiments, in thedetection module 10, the quenchingresistor 4 is connected to the anode of eachSPAD 2. A detection signal is output from the connection point between the anode of eachSPAD 2 and thecorresponding quenching resistor 4 via thepulse converter 6. - Therefore, the
voltage generation module 18 adds the reference breakdown voltage VBD and the predetermined excess voltage VEX to generate a reverse bias voltage VSPAD having a potential higher than that of the anode of eachSPAD 2, and the reverse bias voltage VSPAD is applied to the cathode of eachSPAD 2. For example, since the anode ofSPAD 2 does not have a negative potential, the reverse bias voltage VSPAD is preferably a positive potential. - In contrast, in the
light detector 1F of the present embodiment, as shown inFIG. 6 , in thedetection module 10, the quenchingresistance 4 is connected to the cathode of eachSPAD 2. The detection signal is output from the connection point between the cathode of eachSPAD 2 and thecorresponding quenching resistor 4 through thepulse converter 6. - Therefore, in the
detection module 10, the power supply voltage VB is applied to the cathode of theSPAD 2 through the quenchingresistor 4. In order to operate theSPAD 2 in Geiger mode, the potential of the anode of theSPAD 2 needs to be lower than that of the cathode by the reverse bias voltage. - Therefore, in the present embodiment, the power supply voltage VB is applied to the cathode of the monitoring
SPAD 12 as in theSPAD 2 in thedetection module 10. Thecurrent source 14 is connected to the anode of the monitoringSPAD 12 so as to flow current from the anode to the ground. - Then, the
voltage generation module 18 takes in a negative reference breakdown voltage −VBD lower than the power supply voltage VB from the anode of the monitoringSPAD 12. A negative excess voltage −VEX obtained from the negative electrode side of thevoltage source 16 is added to the negative reference breakdown voltage −VBD. - As a result, in the
voltage generation module 18, the negative reference breakdown voltage −VBD and the negative excess voltage −VEX are added. The reverse bias voltage −VSPAD is thereby generated which is lower in potential than the cathode of theSPAD 2. Then, the generated reverse bias voltage −VSPAD is applied to the anode of eachSPAD 2 in thedetection module 10. For example, in order not to make the cathode of theSPAD 2 have a negative potential, the reverse bias voltage −VSPAD is preferably a negative potential. - Therefore, also in the present embodiment, a reverse bias voltage VSPAD obtained by adding the excess voltage VEX to the reference breakdown voltage VBD is applied between the cathode and the anode of each
SPAD 2 in thedetection module 10. The same effect as that of the above embodiments can be obtained. - Although embodiments of the present disclosure have been described above, the present disclosure is not limited to the above-described embodiments, and various modifications can be made.
- For example, in the first embodiment, it has been described that the monitoring
SPAD 12 may be provided with thelight shielding film 13 for blocking or suppressing the incidence of light. Also in the second to fifth embodiments, thelight shielding film 13 may be provided on the monitoringSPAD 12 to shielding light. In addition, in the case of shielding the monitoringSPAD 12, it is not necessary to provide thelight shielding film 13 as long as light can be prevented from being incident on the monitoringSPAD 12. - In each of the above embodiments, the
detection module 10 has been described as being provided with a plurality ofSPADs 2. Even in the case where oneSPAD 2 is provided in thedetection module 10, the reduction in the detection sensitivity of thedetection module 10 can be suppressed if configured as in the above-described embodiments. - A plurality of functions of one element in the above embodiments may be implemented by a plurality of elements, or one function of one element may be implemented by a plurality of elements. Further, a plurality of functions of a plurality of elements may be implemented by one element, or one function implemented by a plurality of elements may be implemented by one element. A part of the configuration of the above embodiment may be omitted. At least a part of the configuration of the above embodiments may be added to or replaced with the configuration of another one of the above embodiments.
- For reference to further explain features of the present disclosure, the description is added as follows.
- A related art discloses a technology of a light detector using an avalanche photodiode (hereinafter referred to as APD). The technology performs temperature compensation of the APD by using a reverse biased reference junction structure which has a temperature characteristic of the current amplification factor that is almost the same as that of the APD.
- This light detector uses a transistor having a current injection junction structure for injecting a reference current into the reference junction structure, and controls a multiplication factor of the APD by controlling the voltage applied to the APD and the reference junction structure so as to keep the amplification factor of the reference current at a predetermined value.
- The above technology performs the temperature compensation control of the APD by controlling the multiplication factor of the APD. It is thus effective in the linear mode operated by applying a reverse bias voltage less than the breakdown voltage to the APD.
- In contrast, the inventor's detailed investigation has found an issue of the above technology being inapplicable to a light detector that operates an APD in Geiger mode. That is, the APD operating in Geiger mode is called SPAD, and the reverse bias voltage is set to a voltage value higher than the breakdown voltage. Note that SPAD is an abbreviation of Single Photon Avalanche Diode.
- The SPAD used by the light detector breaks down in response to the incidence of photons, and the light detector is configured to output a pulse signal having a predetermined pulse width in response to that the SPAD breaks down.
- Therefore, the output of the light detector using SPAD is “1” or “0”; this type of light detector has no concept of controlling the multiplication factor. For this reason, it is difficult to temperature compensate the detection sensitivity of an SPAD by using the above technique.
- It is thus desired to provide a technology to enable temperature compensation for detection sensitivity of an SPAD, more specifically, the photon detection sensitivity of the SPAD in a light detector using the SPAD.
- Embodiments of the present disclosure described herein are set forth in the following clauses.
- According to an embodiment of the present disclosure, a light detector is provided to include a detection module, a monitoring SPAD, a current source, and a voltage generation module.
- The detection module includes an SPAD that is an avalanche photodiode operable in Geiger mode; the detection module is configured to perform light detection by applying, to the SPAD, a reverse bias voltage in a reverse direction. The monitoring SPAD has characteristics identical to characteristics of the SPAD in the detection module.
- The current source, which may be connected with the monitoring SPAD, is configured to supply a constant current to the monitoring SPAD so as to operate the monitoring SPAD in Geiger mode. The voltage generation module, which may be connected with the monitoring SPAD, is configured to generate the reverse bias voltage to be applied to the SPAD in the detection module based on (i) a reference breakdown voltage set from a breakdown voltage generated across the monitoring SPAD and (ii) a predetermined excess voltage.
- As a result, the SPAD in the detection module receives a reverse bias voltage; the reverse bias voltage is generated based on (i) the reference breakdown voltage estimated to be a breakdown voltage when the SPAD breaks down due to incidence of photons, and (ii) a predetermined excess voltage.
- Therefore, even if the breakdown voltage changes due to the temperature change of the SPAD, the excess voltage becomes a substantially predetermined constant voltage. It is thus possible to stabilize the detection sensitivity of photons by the SPAD.
- That is, in a light detector using an SPAD, a reverse bias voltage exceeding the breakdown voltage is applied to the SPAD; in response to that photons are incident on an SPAD, a detection signal is output based on the current flowing when the SPAD breaks down.
- In contrast, the breakdown voltage of the SPAD changes with temperature. Specifically, the breakdown voltage is higher as the temperature is higher. Therefore, if the reverse bias voltage applied to the SPAD is maintained to be constant, the excess voltage, which is the excess voltage obtained by subtracting the breakdown voltage from the constant reverse bias voltage, becomes lower (decreases) as the temperature becomes higher (increases). The detection sensitivity of the SPAD thereby changes with voltage change of the excess voltage.
- Therefore, in the light detector of the present disclosure, the breakdown voltage of the SPAD in the detection module is estimated as the reference breakdown voltage using the monitoring SPAD. The reverse bias voltage is set based on the reference breakdown voltage and the desired excess voltage.
- Therefore, the light detector of the present disclosure enables the temperature compensation of the detection sensitivity of the SPAD that is included in the detection module, further enabling the light detection with a desired detection sensitivity without being affected by the temperature change of the SPAD.
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US11187575B2 (en) | 2020-03-20 | 2021-11-30 | Hi Llc | High density optical measurement systems with minimal number of light sources |
WO2022035626A1 (en) * | 2020-08-11 | 2022-02-17 | Hi Llc | Maintaining consistent photodetector sensitivity in an optical measurement system |
US11969259B2 (en) | 2021-02-16 | 2024-04-30 | Hi Llc | Detector assemblies for a wearable module of an optical measurement system and including spring-loaded light-receiving members |
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US11296241B2 (en) | 2022-04-05 |
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